Shorter donor leukocyte telomere length is associated with poor peripheral blood stem cell mobilization induced by granulocyte colony-stimulating factor.

BACKGROUND/PURPOSE: Insufficient numbers of peripheral blood stem cells (PBSC) after granulocyte colony-stimulating factor (G-CSF) mobilization occurs in a significant proportion of PBSC collections, often from older age donors. Telomere length (TL) is often used as an indicator of an individual's biological age. This study aimed to investigate the relationship between donors' leukocyte TL and the outcome of G-CSF-induced PBSC mobilization in healthy unrelated donors. METHODS: Donors' leukocyte TLs and the outcome of G-CSF-induced PBSC mobilization, as assessed by pre-harvest CD34+ cell counts, were analyzed in 39 healthy PBSC donors. TL in a non-mobilized general population (n = 90) was included as a control group. G-CSF mobilization effect was categorized into three groups according to pre-harvest CD34+ cell count: poor (≤25/µL, PMD), intermediate (between 25 and 180/µL), and good (≥180/µl, GMD). RESULTS: Leukocyte TL of PBSC donors correlated well with pre-harvest CD34+ cell counts (r = 0.645, p < 0.001). Leukocyte TLs of PMDs (n = 8) were significantly shorter than those of GMDs (n = 9) and non-mobilization controls (p < 0.05). Moreover, all PMD TLs were below the 50th percentile, and 62.5% of PMDs had TLs below the 10th percentile of age-matched control participants. In contrast, no GMD TLs were below the 10th percentile; in fact, 33.3% (3/9) of them were above the 90th percentile. CONCLUSION: Our results indicate that shorter donor leukocyte TL is associated with poor G-CSF-induced PBSC mobilization. TL, which represents a donor's biological age, could be a potential predictor for mobilization outcome.

Dachshund Homolog 1: Unveiling Its Potential Role in Megakaryopoiesis and Bacillus anthracis Lethal Toxin-Induced Thrombocytopenia.

Lethal toxin (LT) is the critical virulence factor of Bacillus anthracis, the causative agent of anthrax. One common symptom observed in patients with anthrax is thrombocytopenia, which has also been observed in mice injected with LT. Our previous study demonstrated that LT induces thrombocytopenia by suppressing megakaryopoiesis, but the precise molecular mechanisms behind this phenomenon remain unknown. In this study, we utilized 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced megakaryocytic differentiation in human erythroleukemia (HEL) cells to identify genes involved in LT-induced megakaryocytic suppression. Through cDNA microarray analysis, we identified Dachshund homolog 1 (DACH1) as a gene that was upregulated upon TPA treatment but downregulated in the presence of TPA and LT, purified from the culture supernatants of B. anthracis. To investigate the function of DACH1 in megakaryocytic differentiation, we employed short hairpin RNA technology to knock down DACH1 expression in HEL cells and assessed its effect on differentiation. Our data revealed that the knockdown of DACH1 expression suppressed megakaryocytic differentiation, particularly in polyploidization. We demonstrated that one mechanism by which B. anthracis LT induces suppression of polyploidization in HEL cells is through the cleavage of MEK1/2. This cleavage results in the downregulation of the ERK signaling pathway, thereby suppressing DACH1 gene expression and inhibiting polyploidization. Additionally, we found that known megakaryopoiesis-related genes, such as FOSB, ZFP36L1, RUNX1, FLI1, AHR, and GFI1B genes may be positively regulated by DACH1. Furthermore, we observed an upregulation of DACH1 during in vitro differentiation of CD34-megakaryocytes and downregulation of DACH1 in patients with thrombocytopenia. In summary, our findings shed light on one of the molecular mechanisms behind LT-induced thrombocytopenia and unveil a previously unknown role for DACH1 in megakaryopoiesis.

Platelet-derived circulating soluble P-selectin is sufficient to induce hematopoietic stem cell mobilization.

BACKGROUND: Granulocyte colony-stimulating factor (G-CSF)-mediated mobilization of hematopoietic stem cells (HSCs) is a well-established method to prepare HSCs for transplantation nowadays. A sufficient number of HSCs is critical for successful HSC transplantation. However, approximately 2-6% of healthy stem cell donors are G-CSF-poor mobilizers for unknown reasons; thus increasing the uncertainties of HSC transplantation. The mechanism underlining G-CSF-mediated HSC mobilization remains elusive, so detailed mechanisms and an enhanced HSC mobilization strategy are urgently needed. Evidence suggests that P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1) are one of the cell-cell adhesion ligand-receptor pairs for HSCs to keep contacting bone marrow (BM) stromal cells before being mobilized into circulation. This study hypothesized that blockage of PSGL-1 and P-selectin may disrupt HSC-stromal cell interaction and facilitate HSC mobilization. METHODS: The plasma levels of soluble P-selectin (sP-sel) before and after G-CSF administration in humans and male C57BL/6J mice were analyzed using enzyme-linked immunosorbent assay. Male mice with P-selectin deficiency (Selp-/-) were further employed to investigate whether P-selectin is essential for G-CSF-induced HSC mobilization and determine which cell lineage is sP-sel derived from. Finally, wild-type mice were injected with either G-CSF or recombinant sP-sel to investigate whether sP-sel alone is sufficient for inducing HSC mobilization and whether it accomplishes this by binding to HSCs and disrupting their interaction with stromal cells in the BM. RESULTS: A significant increase in plasma sP-sel levels was observed in humans and mice following G-CSF administration. Treatments of G-CSF induced a decrease in the level of HSC mobilization in Selp-/- mice compared with the wild-type (Selp+/+) controls. Additionally, the transfer of platelets derived from wild-type mice can ameliorate the defected HSC mobilization in the Selp-/- recipients. G-CSF induces the release of sP-sel from platelets, which is sufficient to mobilize BM HSCs into the circulation of mice by disrupting the PSGL-1 and P-selectin interaction between HSCs and stromal cells. These results collectively suggested that P-selectin is a critical factor for G-CSF-induced HSC mobilization. CONCLUSIONS: sP-sel was identified as a novel endogenous HSC-mobilizing agent. sP-sel injections achieved a relatively faster and more convenient regimen to mobilize HSCs in mice than G-CSF. These findings may serve as a reference for developing and optimizing human HSC mobilization in the future.

Hematopoietic stem cell mobilization.

Hematopoietic stem cell (HSC) transplantation has been used to treat hematopoietic diseases for over 50 years. HSCs can be isolated from bone marrow (BM), umbilical cord blood, or peripheral blood. Because of lower costs, shorter hospitalization, and faster engraftment, peripheral blood has become the predominant source of HSCs for transplantation. The major factors determining the rate of successful HSC transplantation include the degree of human leukocyte antigen matching between the donor and recipient and the number of HSCs for transplantation. Administration of granulocyte colony-stimulating factor (G-CSF) alone or combined with plerixafor (AMD3100) are clinical used methods to promote HSC mobilization from BM to the peripheral blood for HSC transplantations. However, a significant portion of healthy donors or patients may be poor mobilizers of G-CSF, resulting in an insufficient number of HSCs for the transplantation and necessitating alternative strategies to increase the apheresis yield. The detailed mechanisms underlying G-CSF-mediated HSC mobilization remain to be elucidated. This review summarizes the current research on deciphering the mechanism of HSC mobilization.

Correlation of Body Mass Index and Proinflammatory Cytokine Levels with Hematopoietic Stem Cell Mobilization.

This study investigated the correlation of body mass index (BMI) and proinflammatory cytokine levels with hematopoietic stem cell (HSC) mobilization triggered by granulocyte colony-stimulating factor (G-CSF). Stem cell donors (n = 309) were recruited between August 2015 and January 2018 and grouped into four groups according to their BMI: underweight (BMI < 18.5 kg/m2, n = 10), normal (18.5 kg/m2 ≦ BMI < 25 kg/m2, n = 156), overweight (25 kg/m2 ≦ BMI < 30 kg/m2, n = 102), and obese (BMI ≧ 30 kg/m2, n = 41). The participants were then administered with five doses of G-CSF and categorized as good mobilizers (CD34 ≧ 180/µL, n = 15, 4.85%) and poor mobilizers (CD34 ≦ 25/µL, n = 14, 4.53%) according to the number of CD34+ cells in their peripheral blood after G-CSF administration. The correlation between BMI and HSC mobilization was then analyzed, and the levels of proinflammatory cytokines in the plasma from good and poor mobilizers were examined by ProcartaPlex Immunoassay. Results showed that BMI was highly correlated with G-CSF-triggered HSC mobilization (R2 = 0.056, p < 0.0001). Compared with poor mobilizers, good mobilizers exhibited higher BMI (p < 0.001) and proinflammatory cytokine [interferon gamma (IFN-γ) (p < 0.05), interleukin-22 (IL-22) (p < 0.05), and tumor necrosis factor alpha (TNF-α) levels (p < 0.05)]. This study indicated that BMI and proinflammatory cytokine levels are positively correlated with G-CSF-triggered HSC mobilization.

AQP0 is a novel surface marker for deciphering abnormal erythropoiesis.

BACKGROUND: Hematopoiesis occurs in the bone marrow, producing a complete spectrum of blood cells to maintain homeostasis. In addition to light microscopy, chromosome analysis, and polymerase chain reaction, flow cytometry is a feasible and fast method for quantitatively analyzing hematological diseases. However, because sufficient specific cell markers are scarce, dyserythropoietic diseases are challenging to identify through flow cytometry. METHODS: Bone marrow samples from C57BL/B6 mice and one healthy donor were analyzed using traditional two-marker (CD71 and glycophorin A) flow cytometry analysis. After cell sorting, the gene expressions of membrane proteins in early and late erythropoiesis precursors and in nonerythroid cells were characterized using microarray analysis. RESULTS: Among characterized gene candidates, aquaporin 0 (AQP0) expressed as a surface protein in early- and late-stage erythropoiesis precursors and was not expressed on nonerythroid cells. With the help of AQP0 staining, we could define up to five stages of erythropoiesis in both mouse and human bone marrow using flow cytometry. In addition, because patients with dyserythropoiesis generally exhibited a reduced population of APQ0high cells relative to healthy participants, the analysis results also suggested that the levels of APQ0high cells in early erythropoiesis serve as a novel biomarker that distinguishes normal from dysregulated erythropoiesis. CONCLUSIONS: AQP0 was successfully demonstrated to be a marker of erythroid differentiation. The expression levels of AQP0 are downregulated in patients with dyserythropoiesis, indicating a critical role of AQP0 in erythropoiesis. Accordingly, the level of AQP0high in early erythroid precursor cells may serve as a reference parameter for diagnosing diseases associated with dyserythropoiesis.